(a) Field of the Invention
The present invention relates to a nuclide separation type of precipitator system.
More particularly, the present invention relates to an improvement of a wire driving type of precipitator system (hereinafter called a "precipitator" for short) for measuring radioactivities of noble gas nuclear fission products which are produced by a nuclear fission and released into gas.
(b) Description of the Prior Art
A precipitator is an apparatus for measuring radioactivities of a nuclide that is a noble gas nuclear fission product released in case a fuel failure occurs during the operation of a nuclear reactor or when an uranium irradiation test is performed in a nuclear reactor and others, and that its daughter nuclide which is a new nuclide produced by beta-decay of a noble gas nuclear fission product nuclide emits beta-ray in a short time as below a half life of about 30 minutes.
A prior precipitator will now be explained with reference to FIG. 1.
A sample gas 2 containing noble gas nuclear fission products flowing through a sampling pipe 1 introduced into a gas reservoir 3 of the precipitator, in which, when the noble gas nuclear fission product emits a beta-ray, a daughter nuclide newly produced thereby is charged in positive.
Consequently, when applying a negative voltage to a metallic wire 4 placed in the center of the gas reservior 3 by using a high voltage power supply, the daughter nuclide is attracted to the wire 4 and percipitates thereonto.
After being left as it is in the gas reservoir 3 for a given period of time (Ts) for collecting the daughter nuclides, the wire 4 is moved to the position of scintillation detector 6 by a wire-driving mechanism 5, wherein the beta-ray emitted when the daughter nuclide precipitated decays according to its half-life is detected.
The signals detected are divided into noises and beta-ray signals by using a pulse height discriminator 7 and the discriminated signal is input to a counting circuit 8 and is counted.
Generally, the precipitator is used for such a purpose that, when all detectable nuclides are measured as in the fuel failure detection of a light-water type power reactor and it is over a preset value, a fuel failure is regarded as occurring.
In contrast, for the fuel failure detection of gas-cooled type reactor and others in which the difference in the half-life of noble gas nuclear fission products influences the sensitivity of failure detection greatly, or for the precise measurement of noble gas releasing behavior in the fuel irradiation test, such detecting characteristics as being highly sensitive, fast in responsing time and capable of measuring radioactivity for every nuclides are required.
From a viewpoint of separation-measurement of noble gas nuclear fission product nuclides, as shown in FIG. 2, such a method as flowing a gas containing noble gas nuclear fission product through the gas reservoir 1, detecting gamma-ray emission by means of a Ge detector 2 and measuring and analysing it by means of a multichannel pulse height analyzer system 3 to measure radioactivity for all nuclides separately has been generally known.
However, this method has a disadvantage of being so low in detection sensitivity that it is necessary to measure for a long time for obtaining sufficient counts for measuring radioactivity for all nuclides.
And, as a prior art for separation-measurement of noble gas nuclear fission product nuclides by the precipitator, as shown in FIG. 3, a method of utilizing three kinds of delay pipe, and separating the nuclides using only a difference of decrement of noble gas nuclear fission products due to the half-life has been well known.
However, this method also has such a disadvantage that, in order to measure radioactivity of three nuclides separately, three precipitators with uniform characteristics are required, and, for improving the separation-characteristics, it is necessary to take a large delay time so that the difference of decrement of noble gas nuclear fission products due to half-life becomes large, and, since the same time as the delay time is required for obtaining the results, it takes a long time for detection.